1. Field of the Invention
The present invention relates generally to a radar sensor/processor for intelligent vehicle highway systems, and more particularly pertains to a radar sensor/processor for Intelligent Vehicle Highway Systems (IVHS) as promulgated by the Federal Highway Administration, Department of Transportation.
2. Discussion of the Prior Art
There are well in excess of one hundred million vehicles licensed to operate on the highways of the United States, and it has been estimated that at any one time in excess of one hundred thousand vehicles may be wanted for investigation for a variety of reasons. They may have outstanding tickets or violations, exceeded established speed limits, be operating with expired or stolen license plates, or have been at the scene of one or more of many criminal activities. At the present time, license numbers of vehicles wanted for investigation are distributed to local police who, with reference to printed or computerized lists, scan traffic visually encountered in the course of their normal duties. Their task is complicated by the fact that, on a busy multi-lane highway, many different cars constantly pass a given observation point. As a consequence, the probability of intercepting a wanted vehicle is very low.
Attempts have been made in the prior art to automate the surveillance by equipping each vehicle with a transponder device that responds to an interrogation signal by emitting a code that is unique to each vehicle. These interrogation responses are to be presented to an operator who no longer would have to rely on visual observation. These prior art approaches have failed because of the high density of vehicles on highways, particularly suburban areas, and because of the sheer volume of data that is presented to the human observer. For example, on a major highway there can be many more than ninety vehicles within one-half mile of in interrogation device and in a multi-lane environment, many of them will be at the same or nearly the same range and at the same or nearly the same relative velocity with respect to the interrogation device. It has, therefore, not been possible to discriminate the vehicles on the basis of two way signal transit time (radar time) or on the basis of doppler frequency difference. The response codes become hopelessly interleaved, and many vehicles are either not identified it all or are misidentified.
Spiess U.S. Pat. No. 5,264,854 discloses a multiple vehicle identification and classification system which reduces the response rate of the transponder-equipped vehicles by a large factor. The system randomizes in time the responses from a particular vehicle to reduce transponder code interleaving to a negligible level, while retaining the vehicle identification, speed and range information of the data stream. The transponder devices may respond to an interrogation pulse or run free on a randomized basis whenever they are illuminated.
The system utilizes a transponder device the coded responses of which are randomized in time and an interrogation device which processes the return signals to provide vehicle identification, speed, location, and transponder status information on vehicles to an operator, or for storage in memory, or for transmittal to a higher authority.